The invention relates to a sprue-gate configuration, to serve for injection-molding of plastic articles.
In the injection-molding of such plastic articles as bottle caps, a multiple-part mold defines the cavity into which injection is made via a gate orifice in a sprue passage in one of the mold parts. Usually, as in the bottle-cap case, the gate is located at the center of the cavity wall which defines the external surface of the closed end of the molded cap. But, however restricted the gate orifice with respect to the sprue passage, the molded product is marred by a small pointed projection of plastic, at the point of injection, i.e., at the center of the external surface of the closed end of the product. A conventional technique for improving the appearance of the product is to resort to a secondary operation, e.g., cut-off or grinding, but any secondary operation involves expense that should be avoided, and product appearance may suffer from the secondary operation. An alternate technique is so to configure the product contour with a local recess at the point of injection that, upon product extraction from the mold, the small pointed projection will be contained within the volume of the local recess; but, here again, product appearance must suffer, from lack of a smooth external-surface contour.